[quote=@Lucius Cypher]
That's fine with me I suppose. Though I gotta ask: what other free defenses do we get against magic? Can we all see invisible things, block scryers, and are immune to illusions and mind altering stuff too?
[/quote]

... you're the one who specified it can be blocked by nothing less than some sticks, string, and beads. Given that this would also stop unscrupulous pupils from, say, constantly harassing people with nightmares, well, it's not exactly far-fetched.